ROHC (Robust Header Compression) for compressing headers is prescribed in documents such as RFC-4815 and RFC-3095. An example of a control method for controlling wireless communications between base stations which compress headers according to ROHC and mobile stations which decompress compressed headers is disclosed in JP-A 2006-287284 (hereinafter referred to as Patent document 1).
According to the method disclosed in Patent document 1, the restoration ratio of packets which are received from a transmission side by a reception side in a U (Unidirectional)-mode is determined as an arrival ratio, and the information of the restoration ratio is sent to the transmission side, which controls the period at which full headers and dynamic headers, based on the information of the restoration ratio, are sent.